The present invention relates generally to the field of computer driven printer/plotters, particularly wide print media printer/plotters in which paper or other printing media is drawn from a roll thereof in a first direction through the apparatus and a linearly moveable carriage which holds an ink applicator means such as a pen or pens or thermal inkjet printing heads or the like is supported or suspended on a relatively rigid guideway which extends transversely to the direction of paper movement whereby the carriage and print heads may repeatedly traverse the entire width of the paper or other printing medium.
Although it is a relatively straightforward matter to provide a rigid support and suspension mechanism for a print head carriage, to do so without significant expense becomes increasingly difficult as the width of the printing path increases. Printing path widths of three or four feet are not uncommon.
Prior art solutions to the problem include the provision of a carriage guideway which employs two precisely straight and parallel slider rods on which the print head carriage is supported. The rods must be pre-straightened to highly accurate tolerance before installation on the other supporting structure or plotter chassis. The technical processes required to accurately pre-straighten the slider rods are complicated and expensive.
Other solutions to the problem of providing a carriage guideway inlude use of a single precisely straight slider rod in conjunction with machined extrusions or precision sheet metal parts to act as a second reference. Both of these solutions involve high costs due to precision machining requirements and/or specialized fabrication equipment.
In the prior art, the pre-straightened rods or carefully machined rods or rails used to support the carriage are ordinarily suspended only at their ends and are thus susceptible to vibration deflections. For wide print media applications, suspension of the slider rods or rails merely at their ends is insufficient therefore mounting of the rods or rails along their length at intermediate support points is required. The intermediate points of support are typically precision machined on the supporting chassis so that the prestraightened rods are maintained straight at all times. This is not cost effective due to the complicated procedure required to accurately machine and position the support points along the chassis to ensure support of the rods or rails in a perfectly straight orientation.
The present invention is directed to the problem of providing a less expensive means of supporting and holding the carriage rods or rails in an acceptably straight and parallel relationship to ensure proper positioning of the print head carriage as it traverses above the paper or other print media.
Precise positioning of the print head with constant distance between it and the media as the print head traverses the media during plotting is particularly acute in inkjet printing head applications. The guideway and support structure for the carriage disclosed herein is particularly adapted for use with a thermal inkjet printhead although the structure can also be used with plotter carriages other than those which use thermal inkjet printheads.
The present invention accordingly provides a guideway and support structure for a printer/plotter carriage comprising:
a. an elongated beam having a pair of spaced ends; PA1 b. a first generally planar sideplate having a cradle thereon, said sideplate being securely affixed to one of said spaced ends of said beam; PA1 c. a second generally planar sideplate having a cradle thereon, said sideplate being securely affixed to the other of said spaced ends of said beam; PA1 d. an elongated X yoke having stiffness in a first (X) direction of a three dimensional rectangular coordinate system; PA1 e. at least one Z yoke having stiffness in a second (Z) direction of said coordinate system; PA1 f. at least one bridge disposed between said sideplates in a location which divides said beam into approximately equal length sections, said bridge having rod cradles thereon for supporting spaced parallel carriage slider rods extending substantially parallel to said beam; PA1 g. a pair of parallel carriage slider rods supported in said cradles on said sideplates and in said cradles in said bridge; PA1 h. a first set of fasteners clamping said rods to said bridge cradles and to said X yoke and clamping said rods to said cradles on said sideplates; PA1 i. a second set of fasteners affixing said Z yoke or yokes to said beam; and PA1 j. a third set of fasteners affixing said X yoke to said beam.